The creation of large layer-2 domains is a present industry trend. For instance, a datacenter in which host computers are connected to each other using Ethernet or other layer-2 technology is an example of a type of layer-2 domain. In such a datacenter, host computers communicate with each other using their Media Access Control (MAC) addresses. Communication between and among the computers is provided by switches that pass frames to their desired destination MAC address. A larger layer-2 domain may be created by connecting multiple layer-2 datacenters over a layer-3 network, such as the Internet.
Currently, networking technology such as FabricPath™/Transparent Interconnection of Lots of Links (TRILL) and Overlay Transport Virtualization (OTV) attempt to make the scaling of layer-2 beyond its current limits a reality. Each technology has a series of benefits that make it ideal for a certain role in the network. In general, FabricPath™ technology fits well within a data center, while OTV is well suited to interconnect data centers across any transport that is Internet Protocol (IP) enabled. FabricPath™ technology manages information within the layer-2 switches by mapping host addresses to switch identifiers (IDs) in edge devices only, and only on a conversational-learning basis. Therefore, core switches do not build MAC address tables, and edge switches build MAC address tables only for hosts with which they are in communication.
In FabricPath™ technology, a switch associated with a source host receives data from the source host and encapsulates the data to create a frame. The switch creates the frame by adding a header that specifies a switch ID of a switch associated with a destination. The switch at the destination (within the same layer-2 domain) de-encapsulates the data and passes the data to the destination host.
OTV provides a layer-2 connection between two or more layer-2 domains by placing a router at an edge of a layer-2 domain where the router maintains a table of MAC addresses for known hosts. This OTV enabled layer-3 router sends a frame over an inter-connecting layer-3 network (using appropriate overhead) to another OTV router at another layer-2 domain. This is termed “MAC routing.” Hosts within separate layer-2 domains communicate using MAC addresses with the layer-3 routers acting as intermediaries in the layer-3 portions.
Today the two technologies are loosely coupled, which can result in inefficiencies at the hand-off point between the FabricPath™ technology and OTV portions of the network. For example, relatively large amounts of MAC address information may be stored at boundary devices between OTV and FabricPath™ technology. Conventional OTV builds and maintains the MAC address table in the data plane using Application Specific Integrated Circuit (ASIC) hardware memory, which is relatively expensive. An OTV router will seek to build a table of MAC addresses containing the MAC addresses for all of the hosts in each of the connected layer-2 domains, but in a scenario wherein there are many hosts and/or many layer-2 domains, the size of the table can grow prohibitively large. Also, conventional layer-2 Address Resolution Protocol (ARP) flooding may result in an excessive amount of traffic in scenarios where a multitude of layer-2 domains are connected.